Secret signaling



Feb. 23 1926. 1,573,983

R. C. MATHES SECRET SIGNALING Fi-led August 8, 1925 /8 T/ME LA@ DEV/65m) SPEECH vz/5R75? Patented Feb. 23, 192e.

ROBERT CfMATHES, NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COM- ANY, INCORPORATED, 01E NEW YORK, N. Y., A CORPORATION OF NEW Y0 SECRET SIGNALING.

Application led August 8, 1923. Serial No. 656,343.

To all whom, t may concern:

Be it known that l, ROBERT C. MArHEs, a citizen of? the United States of America, residinO at New York, in the county of Bronx 5 and btate of New York, have invented cer'- ta'in new and useful Improvements in Secret Signaling, of which the following is a full, clear, concise, andi exact description.

The present invention relates to the transmission of signaling or other waves, and has particularly to do with obtaining secrecy in such transmission.

It is an object of ythe invention to transmit with secrecy signals or other waves of any desired frequency or other characteristie.

A further object of the invention is to enable multiplex transmission with secrecy in a simple and effective manner.

It has been proposed to divide a mesage wave into its frequency components and to transmit different portions of the wave'so divided over different transmission paths, such as different lines or different carrier 25 or radio channels. To receive the message, the separately transmitted fragments are separately received, or separately detected in the caseof carrier or radio transmission, and are recombined to make up the message waves.

Accordingto the present invention, the message wave is divided as to time rather than as to frequency, and the successive portions of the waves so divided are sent in r rotation over different paths (lines, carrier or radio channels, etc.) Since at least two paths are required, the system lends itself readily to multiplex transmission. Dill'erent messages are divided into successive time-divisions and the successive fragments of different messages are sent in succession over the channels so that each channel is .used practically` continuously for messagetransmission. his not only increases the efficiency of the system over what it would be if two paths were used exclusively for transmitting only one message, but it also makes the system still more secret since the currents which would be received `by anyone attempting to intercept the message y'would be so much the more confusing from having been produced from two different messages.

Briefly and specifically described, the invention may employ commutators for dividing the speech or other waves into successive fragments. yIn the case of a. single messa e,

, the message variations produced during t e time that one commutator segment 1s in circuit may pass directly into the first transmission path. The message variations produced duringthe time that the next commutator segment is in circuit could be arranged to pas immediately into the second path, but it is preferred to supply these variations to a storage device in order to introduce a delay into the transmission of these variations equal to thel time of transit of a commutator segment. lVithl this delay introduced, the variations produced du'ring the transit of the second segment, as described, pass into the second transmission path simultaneously with the production and transmission into the first path of variations occurring during transit of the next .or third segment. With thisy arrangement, there are periods of no transmission over either of the two paths (assuming only two paths) and these periods alternate with periods during which successive portions of a message are simultaneously sent over both paths.

rllhis manner of transmitting the message portions will prevent a listener from receiving an understandable message by receiving simultaneously fromV both transmission paths, as by tappingitwo'physial lines or using sufiiciently broad tuning to, intercept the waves from two carrier channels.

The periods of no transmission of one message may be utilized in an entirely analogous manner for transmitting a second ,message Due, however, to the fact that successive portions of each message are simultaneously sent over different paths, the system does not depend for secrecy upon the continuous transmission of two messages, but'is secret when only one message is being sent.

To receive the message accordin 'to the invention, the portions sent overt e separate paths are separately received and commutated to deliver to each receiver the cornponents of the message intended for that respective receiver, suficient delay being introduced into the proper portions to make them follow the other portions in their e'ect upon the receiver.

While electrical filters may be used in practicing the invention, they are not essen- 60. are connected tolthe modul tor M1 through selection.

The various objects and features of th l invention Will be clear fromthe following detailed-'description of a typical application of the invention to a radio telephone systemas shown i the accompanying drawing.

In the drawing:

Fig. 1 is a schematic representation of a transmitting terminal employing the invention Fig. 2is asimilar representation of the corresponding receiving terminal Fig. '3 shows a form of time lag device that may be used WithA the invention; and,

Fig. 4 .shows a frequency-inverting circuit that mayv be'emp-loyed in conjunction With the system when desired. J

Referring first to Fig. '1, speech currents representing two separate conversations are produced as a result of speakinginto the respective Amicrophones 10 and 11. For convenience,` the message transmitted from the microphone 10 Will be referred to'as the first message and that transmitted from microphone 1.1 will e referred to as the second message. FiltersF, F are shown for conning the frequencies lto a convenient range, such as 200 to 2200 cycles, for example, in

-the case of speech'. l.These filters are not essential but are shown-since it may at times be convenient yto use! them.- These filters may be constructed in accordance ivith the' A10 are applied to the commutator 1.

fand the othercommutator show will be lbe referred to later..

-TIJ2 l through the. amplifier A4.

considered to beF moving to the right `in the drawing. That is, the segments pass to the right across the stationary brushes connected to Lthe respective filter. The segments for each'commuta'tor are numbered 1 to 8 respectively, although it will e obvious to :employ anynumber of segments as may be found convenient.

The even numbered contacts\of commuta- .tor C1 areconnected to the -time lag device ,TL1 Which 4is associated with the amplifier A1'andthe transmitting'modulator M1, to y The odd numbered segments of commutator C1 are connected directly `to the modulatinge-n circuijc.- M2. through the amplifier A1. Conversely, the even numbered segments-of commutator yC2 the amplifier A; and the od numbered segments are connected to the time lag device associated with the modulator circuit I2 The modulator circuit M1 isof the usual and well-known typeof vacuum tube modulator having its grid`or input circuit supplied with theA signaling currents from the amplifiers A1 and A2 and with a radio frequency wave from the source 12. This source 12 may be a machine generator or a vacuum tube oscillator of the type shown in the United States patent to Hartley 1,356,- 763, October26, 1920. 'The outer or plate circuit of the modulator is connected to the .'lhetime lag devices -TL1,'TL1,`etc. mayy eaclnbe of the type shown in Fig. 3 in which the telegraphone wire W is moved at a uni! form speed beneath ythe recording coils R1, R2 and the listening coils L1, L2. Message currents applied to the circuit 14 act through .the coil R1 to impress magnetic variations on the Wire W, and after a time interval depending upon tlie. speed of movement of the "Wire and the distance between. the coils R1 and L1, the message variations are re roduced in the listening coil L1 andppass into he outgoing circuit 15. In a similar manner, a second message incoming on the line 16 is recorded on the Wire W and after a predetermined time interval is retransmitted into the outgoing circuit 17. The coils E, E are erasing coils.

v The operationzof the circuit of Fig. 1 'is-r the tir'st message, that is, from the micr0' y phone 10, are applied -to even numbered segments 8,l 8' of commutator C1 so that as long as the .brush-es are in 'contact With these segments, the speech variations of the first -message are applied to the time lag device TL1. Currents representing the second message are also applied to the even num- Qbered segments'S, 8 of commutator C2 and duringv the time that the brushes are in contact with these segments, these message variations are transmitted directly to the iii modulating circuit M1, Wherecthey modu- .late the carrier or radio frequency Wave and are transmittedto the distant station.

As soon asthe brushes of both commuta- I' torsy advance to engagement with an odd numbered segment, the first message is ap- .plied directly "to the modulating circuit M1,

neously sent over the respective transmitting channels. During this time, the second message 1s applied to the tune lag device TL2 so that this message is not innnediatclytransmitted.

Ina corresponding manner, when the brushes again reach even numbered contacts, the first message is' stored in the delay device TL, and the successive portions .of the second message are simultaneously transmitted over both channels, one portion being sent directly through amplifier A2 and modulator M and the Lother portion coming from the delay device TL2 and being applied to the modulator M2.

The amplifiers A1, A2, etc. serve the additional purpose of preventing reaction of the currents applied to the respective modulators upon the con'unutating and time lag devices, these amplifiers being of the ivell known three-electrode vacuumtube type Which are to a high degree unilateral-ly conducting.

If an unauthorized person attempts to intercept the message by tuning a receiving set to the Wave from only one of the; transmitting antennae, the attempt will be unsuccessful since a single channel carries only fragments of each message Wave and these fragments may readily be made too small to be understandable. Tuning the receiver to receive both transmitted iv'aves simultaneously will yield equally confusingcomponents regardless of whether one orboth messages are being transmitted at any instant. During pauses in one of the conversations, there Will be alternate trans'- mission of energy and no energy in rapid succession due Ato the other-message. As pointedout above, during the transmission periods successive portions of the same message are simultaneously sent so that even though they both are received they will notl combine in the proper mann-er toginerease the intelligibility of the received currents.

The messages are received according to the invention and are renderediintelligible bv n'icans of the circuits shown in Fig. 2 The receiving antennae RA, and RA2 are tuneil respectively to the Waves transmitted from the antennae TA, and TAZ. The radio waves are detected at D, and D., by any suitable type of detectc-'fsuch as'the three' electrode vacuum tube detector. Thesep'arately received and deteeediwaves are, if desired, passed through the filters F. F Which are identical with the corresponding filters of Fig. r1 and are applied to the brushes ofthe corresponding commutators C., and CA. These commutators'are identical with the commutators C, and C2 and are controlled in any suitable manner to run in approximate synchronism with the com# mutators at the transmitting station. .This may be accomplished byl using constant speedmotors to drive the commutatore at the respective stations and in either manually or automatically controlling the commutators at one stationpreferably the re-Il ceiving station, to give the maximum clearn'ess to the received signal.

Currents representing the portion of the first message that was stored in the time lag device TL, are, during the time when the brushes are in contact with an even nu1nbcred segment, applied directly through the unilateral `device A, to the receivers I,. Currents corresponding to the portion of the`v first message which were transmitted directly to the amplifier A, from the computator C, are during the correspondinginterval applied at the receiving station to the time lag device TL, This time lag device is adjusted in the same manner as the dcvice TL, to introduce a delay in the message currents equal to the time of transit of a cominutator segment across the brushes. .-^i.cc rclingly, when the portion :of the message transmitted through lamplifier A5 di. rectly to the receiver R, terminates, the succeeding portion of the message stored in the device TL3 begins to be impressed on the receiver R, So that the current-s representing the first message are continuously impress d on the receiver R,

In an entirely sin'iilar manner, the com- .mutators C .and C, cooperate with the time lag device TL, to impress currents representing the second message continuously upon the receiver R2.

Various changes and refinements may be made in the syttem to suit requirements. For example, instead of using simple modulaters and' detectors, as has been described, the Well-known cari'ier-suppression modulators and detectors (U` S. patent to Carson 1,343,306, June 15, 1920) may be used and either the transmitting and receiving antennfe may be tuned to confine the transmitted components to a single eide band, or a succesi've modulation system, such as is shownin U. S. patent to Osborne 1,361,488, Decem her 7, 1920, may be employed to obtain a single 'side band for transmission. Instead of transmitting two separate carrer Waves and relying on frequency selectivity between `the radio frequencies to separate the re'jpective message". at the receiver, the messages mav modulate two intermediate frequencies of the same carrier Wave and the frequency selection fnay be made after detection of the received wave as is shown, for example. in British Patent 132,562. i

Instead of using radiated Wavesfor transmission of the re"pective message variations, the carrier waves maybe applied to a line f comprises an inveerting modulator M3 of the phones or, if desired, the two or more transmission paths may be separate physical line circuits.

As a further modification to increase the degree of secrecy, the frequency inverting circuit of Fig. 4 may be inserted in the circuit at both the transmitting and receiving stations. The circuit Fig. 4 may be inserted at each of the points B, B by merely opening the circuit at each of these points in Figs. 1 and 2 and connecting the lefthand terminals of Fig. 4 to the left-hand side of the severed circuit and the 4righthand side of Fig. 4 to the right-hand side of the severed clrcuit in each of these figures.

The speech inverting circuit of Fig. 4

type shown in U., S. patent to` Hartley 1,419,562, J une 13, 1922, to the input or grid circuits of Which may be applied speech currents together With a wavefrom the source 18 of'continuous Waves having a frequency near. the upper limit Vot essential speech frequencies, for example, 2400 cycles. The inverting action of this circuit When used in connection with the systems of Figs. 1y and 2 may be explained more clearly by the following numerical example: Assuming that the continuous Wave from source 18 has a frequency of 2400 cycles, the incoming speech waves from the vrespective micro- 10, 11 of Fig. 1 or from the detectors D1, D2 of Fig. 2, received by the speech inverter may comprise a component of 200 cycles which modulates the 2400 cycle Wave to produce an upperA side band component of 2600 cycles and a'lower side band component of 2200 cycles. Assuming that the filters F transmit only frequencies from 200 to 2200 cycles, the 2600 cycle component Will be suppressed and only the 2200 cycle component Will be transmitted. `Similarly, an incoming component having a frequency of 2200 cycles Will be transmitted as a component of onlyJ 200 cycles. The frequency order of the components.- is therefore reversed in passing through the circuit of Fig. "4: i

It is found tha-t inverted speech frequencies thus produced are practically incapable of being understood so that if they are employed the commutatore may be 'run much more Slowly 'Without permitting any intelligible fragments to be transmitted, and the secrecy of the systemniay be markedly increased.

lVhile' the system has been described m connection with speech transmission it is applicable to the transmission of waves or currents of any desired character, suoli 'as telegraph. curre-nts"and the like. I

I claim 1. The method v,of wave transmission-com prising separating the Waves into successive portions and simultaneously transmitting the successive portions over diderent respective transmission paths? v 2. The method of Wave transmission com- 'prising separating the Waves into successive portions of equal duration and simultaneously transmitting the successive portions over different respective transmission paths. 3..'l`he method of secret transmission of 'ya .message comprising producing current variations corresponding to the message variations, mechanically dividing the current variations into successive portions occurring in time, and `simultaneously transmitting over a plurality of distinct 'paths successive portions of the current variations.

4. The method of secret transmission of a message comprising producing current variations representing the message, switching successively produced portions of the current variations into difl'erentcircuits and si- Inultaneously transmitting over a pluralityy 'a different transmissionchannel after a de-v lay e ual to one of said periods.

7. lhe method of secret multiplex transmission comprising transmitting successive portions 'of one message over respective transmission paths simultaneously, and thereafter transmitting successive portions of" another message over the same respective paths simultaneously.

8. The method of secret multiplex transmission comprising producing separate message Waves, introducing a time lag into the transmission of certain portions of each message Wave, transmitting in turn another portion of each message over one transmission path and transmitting over a different path simultaneously the delayed portion of the same message.

y 9. The method of secret signaling comprising inverting the frequency order of the message Waves and simultaneously transmitting over different transmission paths successive portions vof the 'inverted' frequency 1 Waves.

10 The method ofl receiving successive portions of message Waves simultaneously sent over different paths comprising impressing certainof the received Wave portions directly upon a receiver and impressing other received portions u on the same receiver after a time lag s cient to bring the different ortions into non-overlapping re1a tion in t e proper order to reproduce the messa e intelligibly.

11. he method of secret telephony comrising dividing speech waves on a time asis, simultaneously transmitting successively produced speech components over different transmission paths, and at a receiving point producing successively occurring speech components from the simultaneously received components.

l12. In a secret signaling system, a plural.- ity of transmission paths, means to produce signalvariations to be transmittedz means to divide said variations into successive portions, a distributor for directing successive portions of said variations to dilerent' ones of said transmission paths, and a time lag device connected between said distributor and one-.of said paths to cause the portions of the signal varlations transmitted over the path to 'overlap in time the portions transmitted over another path. v

13. In a secret signaling system, means to produce signaling current variations, means to divide said variations into successively occurring portions, and means to transmit successive ortions of said variations si# multaneous y over different transmission paths.

14. In a secret signaling system a plurality of transmission paths, means to produce message currents, and means including a distributor and a storage element for simultaneously impressing on. said paths successively produced message current components.

15; In a secret multiplex signaling system, a plurality of transmission paths, means to roduce current variations representing diferent messages, and means including distributors and time-lag devices for simultaneously impressing on said paths successively produced`current components of one message, and impressing on said paths alternately with said simultaneously impressed components, successively produced components of the other message.

In Witness whereof, I hereunto subscribe R BERT MATHES. 

